The growth of marine organisms on structures exposed to fresh or salt water is a problem having both practical and aesthetic aspects. Typical marine growth commonly involves both plants and animals such as sea moss, various forms of algae, acorn shells, goose muzzles, barnacles, tube worms, etc. Marine growth can be unsightly and can reduce the operating efficiency of marine equipment such as heat exhangers, gates, dry docks, ships, pipelines, etc.
A major problem relates to marine growth on ships' hulls. Marine organisms in substantial accumulations on ships' hulls can increase the energy needed to propel a ship leading to either an increase in fuel consumption or substantial reduction in ship speed. Marine organisms accumulate on exposed hull surfaces at a rate such that they cannot be economically removed in dry dock.
One alternative which has been attempted in the past involves applying to the ship's hull or other marine structure a coating that incorporates a biocide which is slowly released at the surface of the coating to form a concentration lethal to the organism.
Useful marine anti-fouling coatings or paints must form a hard, flexible, relatively smooth film that can remain uncracked and unblistered for an extended period of time of up to five years or more. Further, during its useful life, the coating must provide an effective marine biocidal concentration of a biocidal composition at the surface of the coating that can prevent the accumulation or growth of marine organisms.
Many such coatings have been proposed. The following is a discussion of representative types.
Sparman, U.S. Pat. No. 2,970,923 teaches essentially monomeric tri-substituted methyl halides which can be used in coating compositions. James, U.K. Pat. No. 1,124,297 teaches an anti-fouling coating composition comprising an organotin-containing polymer vehicle and a water soluble pigment which in combination can increase the biocidal efficiency of the coating. Leebrick, U.S. Pat. No. 3,167,473 teaches homopolymers and copolymers of trialkyl tin methacrylate in an anti-fouling coating composition containing a vinyl resin, an acrylic resin or an alkyd resin vehicle base, pigments, thickeners, fillers, or driers blended in commonly available solvents. Hopewell, U.S. Pat. No. 3,575,123 teaches hydrophilic acrylic resins made from a hydrophilic acrylic monomer containing in the polymer matrix essentially monomeric organo metallic compounds such as trialkyl tin halide, triaryl tin halide, and others. Hopewell teaches that the hydrophilic acrylic resin can be crosslinked to reduce the resistance experienced by moving watercraft. Dennington, U.S. Pat. No. 4,139,515 discloses an aqueous emulsion of a copolymer of a triorganotin salt of an olefinically unsaturated carboxylic acid and another unsaturated comonomer in combination with a substantially water insoluble metal containing pigment that is capable of reacting with sea water to form a water soluble metal compound. Matsuda, U.S. Pat. No. 4,157,999 teaches a novel copolymer containing copolymerized units of a substituted tin monomer and a specific aromatic monomer. DeGraff, U.S. Pat. No. 4,221,839 teaches combining essentially monomeric toxic solid organo metallic compounds with a water insoluble binder and a water soluble binder in order to produce a coating composition which in response to the mechanical action of the water, wears at a sufficient rate to release an effective biocidal concentration of the organo metallic. Dawans, U.S. Pat. No. 4,262,097 teaches an organo metallic polymer composition which is formed by grafting onto a main chain consisting of a chlorinated polymer, at least one chain of recurring units of an organotin monomer. Watanabe, U.S. Pat. No. 4,314,850 teaches an antifouling coating composition containing an essentially monomeric triaryl tin compound, a resinous vehicle and an organic solvent.
In our developmental efforts we have found that by following the directions of the prior art and forming anti-fouling coating compositions from a homopolymer or interpolymer of a trialkyl tin acrylate compound and blending the homopolymer or interpolymer with a solvent, vehicle, filler, thickener, or pigment, the resulting compositions over an extended period of time either cannot form a hard, flexible, stable coating which can survive the marine environment or cannot provide an effective biocidal amount of trialkyl tin compound to prevent the growth or accumulation of marine organisms.
Accordingly, a substantial need exists for a coating composition which can be applied to marine surfaces that can survive intact in the marine environment without substantial cracking, blistering or peeling and can provide an effective biocidal concentration of the trialkyl tin compound at the surface of the coating for an extended period of time.